Fuel system shout-off valve closing time
I really hope that somebody can help me.
I need to find closing time
for fuel system shut-off valve (Any valve but best of all would be for
motor controled ball valve). Could anyone tell me how to do it or tell
me where I can try to find some information?
I have a belief that it is possible to calculate but I heed your help.
Valve shut off times are critical in systems as they can cause
waterhammer events that can be destructive. In the extreme you have the
disconnect valves on air bourne refuelling tankers. The break away
coupling produces massive pressure spikes. (ref Swaffield & Boldy).
A motor controled ball valve can be used on facilities for shipunloading or loading.
Just confirming what PeterIgg has posted. For fuel supply to burner
management systems, the typical closing time required is 1 second. A
few allow up to 5 seconds for the system, but when you break it down
into each action that has to happen for the signal to be sent to the
valve to close, it leaves around 1 second for the valve to shut. Most
of fuel shut-off valves in burners are fairly small ball valves. 1 and 2
inch sizes. Can get as small as 1/2 inch pipe sizes. For larger
burners, they can get up to 8 inch. Hundreds of thousands of ball
valves used in these applications all over the world and all of them
closing this fast. So don't get derailed by waterhammer and other
misdirections.
Most are pneumatically operated to open with
spring closure. Solenoid valve control the air in/out. Can't think of
any electric operator that can close a ball valve in 1 second. Hydraulic
operation can achieve these speeds, but is very expensive and messy.
What
is used on burner management systems is probably too large for
aircraft. If your pipe size is less than 1/4 inch, you have reached the
low size limit to practically make a ball valve.
For your project, it can be calculated fairly easily using a ball valve with spring return pneumatic actuator. Break the 90 degree rotation into steps. Say 10 steps between full open and closed. At step one, the valve is full open. You know the fluid properties and flow rate, but you also need to know the upstream and downstream pressures. First assumption, do the upstream and down stream pressures remain constant or do they change as the valve closes to a higher maximum differential pressure when shut. Make a graph of DP versus valve position so you can calculate the flow through the valve at each step of closing. Now for the speed of closing. You have to know an appropriate actautor size so you know the spring force and air volume inside. You also have to know the Cv of the solenoid exhausting the air. First step on time is to determine the delay. How long for the solenoid to shift and how long for excess air pressure to vent before the actuator starts to rotate. Add to this the time it takes to each increment of air volume to exhaust from the cylinder knowing the pressure in the actautor at that point. Add up all the times plus the delay and you will be very close to the actual time.
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